Method of removing gloss from magnesium mold surface



y 1966 R. s. MEICCAFFRAY, JR.. ETAL 3,

METHOD OF REMOVING GLOSS FROM MAGNESIUM MOLD SURFACE Filed Jan. 13, 1964I Z "I: Z :Q Z

INVE TORS' 13 1% tT//4 s ATTORNEY-5 United States Patent 3,248,825METHOD OF REMOVING GLOSS FROM MAGNESIUM MOLD SURFACE Rex S. MacCaffray,Jr., Boiling Springs, and Kenneth E. Hankins, Carlisle, Pa., assignorsto C. H. Masland & Sons, Carlisle, Pa., a corporation of PennsylvaniaFiled Jan. 13, 1964, Ser. No. 337,433 7 Claims. (Cl. 51-481) The presentinvention relates to a method of treating the molding surface of amagnesium or magnesium alloy mold to reduce the lustre and produce auniform surface.

The purpose of the invention is to brush the molding surface of amagnesium alloy mold with an alkaline abrasive compound in a slurry in asuitable liquid such as water at or below ambient temperature to removeany surface film which may have resulted from etching of the surface andproduce a surface having less lustre and more uniformity.

A further purpose is to protect a magnesium or magnesium alloy moldsurface While it is exposed to Water and while it is being abraded, byan alkaline solution, suitably containing zinc oxide in dispersion.

A further purpose is to stabilize the molding surface of a magnesium ormagnesium alloy mold.

A further purpose is to produce a controllable degree of delustering ofthe mold surface.

A further purpose is to improve the surface appearance of productsmolded in a magnesium or magnesium alloy mold by removing a coatingwhich tends to form on the surface and which produces a variable highgloss on the molded object in different areas.

A further purpose is to rub the scrubbing brush over a cake of suitablealkaline soap, for example Fels Naphtha or P & G laundry soap, beforeapplying it to the slurry in the mold, thus increasing the alkalinity,aiding in dispersing the zinc oxide or other abrasive, acting as adetergent to remove oil and grease from the surface and tending toprotect against any corrosive action which might be exerted by chlorineor the like in city water.

A further purpose is to incorporate in the slurry from 0.2% to 15% onthe Weight of the solids of a hard abrasive such as aluminum carbide orsilicon carbide in a size range below 100 microns and preferably in asize range of 50 to 100 microns and thus accelerate the speed ofabrading.

Further purposes appear in the specification and in the claims.

The drawing is a diagrammatic transverse section of a magnesium ormagnesium alloy mold which is useful in explaining the invention.

For many purposes it is desirable to mold plastic against a basematerial, which may be Wood, metal, paper fiber, textile material, or ofsome other character, whether in the partially prepared or finishedform. For example, plastic moldings may be applied on furniture, ondoors,

windows, chair rails, or other building components, on

paper for reinforcing or ornamental purposes, on fiberboard forornamental or reinforcing puposes, and on textile fabics, particularlycarpets and rugs, for reinforcing on places of exceptional wear, as forexample stair treads and risers, entrances to rooms, and in front offurniture and the like where frequent wear is encountered. In the makingof automobile carpet it is common practice to apply protection to thesurface of the carpet at locations where the heel of the drivers footwill be placed and other locations where executive wear might beencountered.

It has previously been discovered that formulations of plastic, rubberor synthetic rubber can to advantage be molded on the surface of a basematerial such as carpet, wood fiber, paper, metal or the like.

The material used is generally referred to as a plastic and may be ofany of the well-known types, such as phenol-formaldehyde,urea-formaldehyde and others of the thermosetting plastics, or it may beone of the thermoplastics including polyvinyl chloride, polyvinylacetate, polyvinyl chloride acetate and also it may be one of theelastomeric materials similar to rubber or synthetic rubber includingbuna S, buna N and others. Olefinic plastics of the type of polyethyleneand polypropylene may also be used.

For many purposes the most widely used plastics for these applicationsare polyvinyl chloride plastisols, of the character well known in theart which are gelled and fused under heat preliminary to cooling, atwhich time they adhere to the fabric to form a solid plastic.

As shown in the drawing, very desirable molds are obtained frommagnesium or magnesium base alloys. The alloys are or more percentmagnesium, usually percent or more magnesium, the balance being smallalloying additions of such metals as aluminum, zinc and manganese.Typical magnesium alloys of which the molds are desirably made are PEalloy which contains 3.25 aluminum and 1.2 percent zinc, the balancebeing magnesium, all percentages being by weight. Another suitablemagnesium base alloy for making such molds in AZ31B which has a nominalcomposition by weight of 3 percent aluminum, 1 percent zinc and 0.2percent manganese, balance magnesium.

These alloys are commonly machined by chemical machining, etching with asuitable acid, desirably dilute nitric acid, usually according totechniques described in one or more of the following patents:

Easley and Swayze, U.S. Patents 2,940,763 to 2,940,- 767; Hopkins andEasley, U.S. Patent 2,828,194; Fishaver, U.S. Patent 2,940,836; Easleyand Hopkins, U.S.

Patent 2,979,387; and Easley and Fishaver, U.S. Patent.

It will be evident also that the mold can be mechanically machined inwhole or in part.

One of the undesirable effects of the process of manufacture previouslyemployed is that the mold has an uneven glossy or shiny surface whichproduces a variable undesirable glossy surface on the plastic molding.

One of the problems presented is that further etching techniques whichmight remove this surface may present the difficulty of loss inrefinement of detail of the contour or corrosion of the magnesium ormagnesium alloy. Furthermore, if the usual etching techniques are usedfor this purpose, While they remove the objectionable layer, they createan objectionable glossy surface themselves.

We have discovered that it is possible to remove the variable glossylayer while protecting the molding surface of the magnesium or magnesiumalloy against corrosion and at the same time to produce a very desirableuniform less lustrous surface.

In the preferred embodiment of the invention we pour on the activesurface of the mold a slurry of finely divided alkaline abrasive in asuitable liquid, preferable water.

The abrasive is preferably zinc oxide, but other suitable alkalineabrasives Which may be used are magnesium oxide, magnesium carbonate orcalcium carbonate. The alkaline abrasive should :be finely divided, thatis, it should have a mesh of a size of 0.5 to 5 microns and preferably0.5 to 1 micron, and the particles should be free from sharp corners.

In addition to the alkaline abrasive it is desirable to use a soap,suitably a commercial laundry soap having excess of alkali (Fels Naphthaor P & G soap is a suitable example). This performs the functions ofremoving oil and grease, dispersing the abrasive, and furthermaintaining the alkalinity and protecting against any harmful effectfrom chlorine or other components in domestic water supplies. Thequantity of soap should be sufiicient to give a little lather. Otherdetergents should not be used as they may attack the magnesium. In somecases it is desirable also to add a hard abrasive of the character ofaluminum carbide or silicon carbide, which should be present in therange of from 0.2% to 5% of the total solids in the slurry, thepercentage being measured by weight. The particle size is the finestsuitable for optical grinding, which is desirably of a size of 50 to 100microns. The hard abrasive speeds up delustering.

It is advisable to use water and abrasive at or below ambienttemperature, so as to reduce undesirable activity by way of attackingthe magnesium.

Instead of Water, other suitable liquids can be used, such as ethylalcohol, methyl alcohol, Stoddard solvent and any other liquid whichwill not injure the magnesium surface under the conditions.

The action of the liquid is intended to be physical rather than chemicalas it functions as a carrying medium.

The abrasive is mixed in the liquid in great excess to form a slurrywhich will suitably be of milky or creamy consistency.

The preferred technique is to place the active mold surface horizontaland uppermost, pour the slurry of alkaline abrasive and liquid on themold surface, and then to rub it manually with a brush. The preferredbrush is a nylon bristle scrubbing brush of the character well known inthe art and commonly used for scrubbing fixtures and floors in thekitchen and bathroom. Brushes of tampico fiber were used with success,but they deteriorated rapidly. Pig bristle brushes may also be used. Thebristle size is suitably of the order of 20 to 50 denier.

We find that the brush strokes should preferably be in the advancingcircular direction and the downward force on the brush should be of theorder of 5 to 15 pounds per scrubbing brush.

Example I A magnesium alloy mold 20 of PE alloy of the shape shown inthe drawing has an active mold face 21 produced by chemical machining oretching, surrounded by a rim 22. Active mold face 21 has numerouscontours or projections 23 which are intended to form recesses in themolded object.

As produced it has an objectionable nonuniform gloss on the activesurface which is believed to be due to a coating which forms as a resultof the chemical etching or other machining.

We pour into the mold and on the active face a slurry 24 of milkyconsistency of ordinary city tap water and zinc oxide shaken up atambient temperature. The particle size of the zinc oxide was 0.5 to 1micron, rounded corners. The slurry is rubbed with a nylon bristlescrubbing brush using an advancing rotary motion and a downward force ofabout lbs. The time taken in scrubbing each portion of the surface isabout five seconds and the total time therefore depends on the size ofthe mold.

The result obtained is that the active face of the mold is of reducedand more uniform gloss Without any appreciable change in dimension andwithout any loss in definition of the contours 23. The surface insteadbecomes uniform which produces a similar uni-form finish on the moldedheel pad or other object.

Example II An attempt was made to add various anionic detergents in theprocedure of Example I and it was found that they were unusable :becausethey immediately marked the surface. Trisodium phosphate and variouspolyphosphates proved to be bad.

4 Example III In applying the technique of Example I the wet brush wasrubbed over an alkaline laundry soap, of the character of Fels Naphthasoap or P & G laundry soap, when first applying it to the mold. Thispromoted the Wetting of the magnesium surface and reduced the time ofprocessing appreciably.

Example IV The technique of Example I was carried out except that from0.2% to 15% of a hard grit on the weight of the solids was incorporatedin the slurry. The hard grit used was optical aluminum carbide abrasivehaving a particle size of the order of 50 to microns and in one exampleit formed 5% of the solids. This reduced the time of the operation tothe extent of about /2 and further reduced the gloss.

Example V The technique of Example I was carried out using the soapaccording to Example III and using the hard abrasive according toExample IV. This further slightly cut the time of the operation.

Example VI The procedure of Example I is carriedout using sodiumbicarbonate instead of zinc oxide. The action in making the lusteruniform is less rapid than in the case of Example I.

Example VII The procedure of Example I is carried out using sodiumcarbonate instead of zinc oxide. The action is similar to that inExample I except that it proceeds less rapidly.

In view of our invention and disclosure variations and modifications tomeet individual whim or particular need will doubtless become evident toothers skilled in the art, to obtain all or part of the benefits of ourinvention without copying the method shown, and we therefore claim allsuch insofar as they fall within the reasonable spirit and scope of ourclaims.

Having thus described our invention what we claim as new and desire tosecure by Letters Patent is:

1. A method of reducing and making more uniform the lustre on a moldsurface of a mold of the class consisting of magnesium and magnesiumalloys, which comprises scrubbing the mold surface with a brush in thepresence of a slurry of an alkaline abrasive in a liquid to modify thesurface and produce a uniform finish of lower lustre.

2. A method of claim 1, in which the alkaline abrasive is a material ofthe class consisting of zinc oxide, magnesium oxide, magnesium carbonateand calcium carbonate and the liquid is water.

3. A method of claim 2, which comprises further introducing an alkalinesoap into the slurry.

4. A method of claim 3, which comprises further incorporating into theslurry from 0.2% to 15 of a hard abrasive of a particle size not inexcess of 100 microns.

5. A method of claim 1, which comprises incorporating into the slurry analkaline soap.

6. A method of claim 1, which comprises incorporating into the slurryfrom 0.2% to 15 of a hard abrasive having a particle size finer than 100microns.

7. A method of claim 1, which comprises scrubbing with an alkalineabrasive of the class consisting of zinc oxide, magnesium oxide,magnesium carbonate and calcium carbonate in water at a temperature notin excess of ambient temperature.

LESTER M. SWINGLE, Primary Examiner.

1. A METHOD OF REDUCING AND MAKING MORE UNIFORM THE LUSTRE ON A MOLDSURFACE OF A MOLD OF THE CLASS CONSISTING OF MAGNESIUM AND MAGNESIUMALLOYS, WHICH COMPRISES SCRUBBING THE MOLD SURFACE WITH A BRUSH IN THEPRESENCE OF A SLURRY OF AN ALKALINE ABRASIVE IN A LIQUID TO MODIFY THESURFACE AND PRODUCE A UNIFORM FINISH OF LOWER LUSTRE.